Surgical Heart Block

Complete atrioventricular dissociation caused by injury to the bundle of His is a serious complication of intracardiac operations. This conduction defect restricts the ability of the heart to increase cardiac output by means of increased ventricular rate. Such restriction may be relieved by drugs or electrical stimulation.¹,³,⁵,⁸,¹⁰⁻¹² This investigation was designed to appraise the effects of electrical stimulation, variations in temperature, isoproterenol, and digitalis in dogs with complete heart block. Methods In 20 mongrel dogs, complete heart block was induced by ligation of the bundle of His during a brief period of inflow occlusion under light thiopental sodium anesthesia.³,⁶Fifteen animals were studied at the time of this procedure. Five were allowed to recover and reanesthetized for study 2 days later. Measurements were made of mean systemic arterial pressure, cardiac rate, mean left atrial pressure, and cardiac output by a dye-dilution technique.⁴Left atrial pressure was regulated